Variable resistor adjustable electrical instruments



Nov. l1, '1958 M. E. BOURNS EI'AL VARIABLE RESISTOR ADJUSTABLE ELECTRICAL INSTRUMENTS Filed May 2, 1957 /QlcHAD E" United States Patent O VARIABLE RESISTR ADJUSTABLE ELECTRICAL INSTRUMENTS Application May 2, 1957, Serial No. 656,556 1 Claim. (Cl. 201-56) This invention relates to new and improved adjustable electrical instruments, and more particularly to adjustable electrical instruments such as potentiometers which are specifically designed so as to be capable of being used in very small devices such as, for example, hearing aids.

The past several years have seen a very drastic change in the design of hearing aids. Formerly conventional hearing aids were comparatively bulky structures which had to be carried in some sort of a pocket or other receptacle upon the clothing of an individual. The advent of transistors and transistorized circuits has made possible a very definite reduction in size in hearing aids. Commonly at the present time the principal operative parts of a hearing aid are disposed in extremely small containers or in parts of glasses or the like so that they may be conveniently worn by an individual.

Potentiometers are used in hearing aids in order to vary the volume level of sound produced. In general terms, it may be concluded that potentiometer development has not kept pace with the development of hearing aids since hearing aids commonly marketed at the present time use essentially the same type of potentiometers formerly employed. A common type of rotary potentiometer used for volume control in many hearing aids at the present time is about 5/s to 3%" in diameter, and is approximately 1A" thick. Obviously this size is inconvenient for many of the present applications. Also conventional potentiometers such as rotary potentiometers used with hearing aids are objectionable because of the knob-type arrangements used for adjusting these instruments and because of certain other structural details. In general the very prior potentiometers tend to be noisy because of a number of reasons such as reasons related to the type of resistance elements utilized and because of other structural details.

A broad object of the present invention is to produce new and improved potentiometers which are specically adapted for use with hearing aids and other types of similar devices. Another object of the present invention is to provide potentiometers of this category which include a switch mechanism carried by and actuated by parts of these instruments. A still further object of the present invention is to provide new and improved potentiometers which are extremely reliable in use and which may be easily and comparatively inexpensively constructed.

Another extremely important object of the present invention is to provide potentiometers which can be formed in a variety of dierent manners so as to provide for linear or non-linear or functional adjustment of electrical values, during adjustment of these instruments in a uniform or linear manner. Thus, for example, it is possible to provide hearing aid potentiometers achieving functional outputs corresponding to the so-called audiotaper. This term is commonly used in the hearing aid field to designate a certain type of volume control. Another object of the present invention is to provide potentiometers for hearing aid and other uses which overcome many of the other disadvantages and limitations of 2,860,214 Patented Nov. 11, 1958 ice 2 conventional hearing aid and other potentiometers as indicated broadly in the preceding discussion.

Still further objects of the invention as well as many specific advantages of it will be more fully apparent to those skilled in the art to which this invention pertains from a detailed consideration of the remainder of this specification including the appended claim and the accompanying drawing in which:

Fig. l is a perspective view ofv a potentiometer of this invention;

Fig. 2 is a cross-sectional view taken at line 2-2 of Fig. l;

Fig. 3 is a cross-sectional view taken at line 3-3 of Fig. 2;

Fig. 4 is a cross-sectional view taken at line 4-4 of Fig. 2; and

Fig. 5 is an exploded perspective view of the potentiometer showing in Fig. l.

It is to be understood that the accompanying drawing is not to be taken as limiting this invention in any respect.

This drawing is primarily intended so as to clearly indicate the nature of a presently preferred embodiment of the invention. Because of the purpose of the drawing it does not represent any precise commercial unit drawn to scale. Obviously instruments falling within the scope of this invention having a different appearance may be manufactured by altering a number of structural details without departing from the essential features of the invention as herein explained.

As an aid to the understanding this invention it may be stated in essentially summary form that it involves adjustable electrical instruments such as' potentiometers, each of which is built to include a resistance element disposed upon a non-conductive member in such a manner that portions of the resistance element along its length extend in a curved path from and around the non-conductive member and from the rest of the resistance element. With the invention a contact member is rotatably mounted adjacent to su'ch a resistance element, and curved contact means extending around the resistance element are provided so as to engage different parts of these projecting portions of the resistance element as during movement of the contact member so as to adjust an electrical value. Constructions of this category diier from a number of different prior constructions in that a definite curved pat or line for electrical contact between the parts is provided on both the resistance element and the contact member for use establishing electrical communication between these two operative parts.

The actual details of this invention are best more fully explained by referring directly to the accompanying drawing. ln Fig. l there is shown va perspective view of a complete hearing aid potentiometer 10-l of the present invention which is built so as to include end caps 12 between which there is rotatably held a non-conductive cylindrical housing 14. If desired the exterior of this housing may be linut-led or serrated so as to aid in the adjustment of the potentiometer 10. Preferably the end caps 12 are each formed out of a non-conductive material such as an appropriate phenolic resin so as to each include a flat bottom surface 16 which is adapted to rest upon appropriate mounting surface (not shown) such as a printed circuit terminal board. Within the center of each of these end caps 12 there are provided openings 18 which are adapted to hold naillike fasteners 20.

As indicated in Fig. 2 of the drawing the fasteners extend from the openings 18 into a central opening 22 in a cylindrical non-conductive member 24 and serve to hold this non-conductive member 24 within interior cavities 26 formed in opposed sides of the end caps 12 so as to space these end caps from one another. As is best indicated in Fig. 2 ofthe drawings the non-conductive member 24 in- 2,860,214 j v Y ycludes a ridge 28 `formed -around the exterior thereof betweenthe end caps 12. Preferably this ridge 28 is molded integrally with the member 24, although if desired, it may take the form of a simple Anon-conductive wire secured .tottheexterior of the member -24 by conventional means such as,.for.example,endsof `such a Vwireviitting withinholes lin this member 24. Preferably the edge of theridge 28 furthest removed fromthe member 24 should be accurately .formed-so that this edge is always spaced at algivendistance .from the axis of the housing 14 in order.to.insure=proper operation ofthe potentiometer 16.

Around the exterior of the member 24 and the ridge 28 there is located a vwound resistance element 3@ which is preferably formed of comparatively ne, accurately dimensioned .Wire isuch as, for Vexample appropriateNichrome Wire. The ends of this resistance element are .attachedfttomire-terminals -32 whichg--asshown in Fig. l2 of the drawing, iit within grooves 34 in the member 24heneath-endslof theelemcnt 30 and which extend from these grooves 34 through appropriate openings'36in-the Vendcaps 12. The resistance element Btl-may be attached to the terminals 32 by various conventional meansfsuch asabyithe. use of solder.

4Ontheinterior .of the housing 14 there is formed an elongated projection 38 which is adapted to iit within notches 40 in the ends 42 of a contact member 44. As is best Vseen ,in ;Fig..5 of the drawings these ends 42 each have.the essential shape of a washer, and these ends are connectedby meansof awall46 whichiits closely against the-interiorlofihehousinglt. .Between the ends 14 there vtitenjds :a resilient metalcontact element 48 having essentially-fa U.-shape as indicated in Fig. 2 of the drawings. This contact element 48 is connected to-both the ends 42; furthenlhefwall 46 s Vattached to it in order to give the contact element .48 ksuflicient rigidity so that the satisfactory .operation of vthe potentiometer may be achieved. IPreferably:the contact member 44 is formed ofaresilientmetal.

Abowedspringalike'washer 52'is located within one-of the .cavities 26 in. onef.of the end caps Vv1-2 so as to resilrnernher-44gas1ndicated in Fig. 2 of the drawings. Qtherwireflike terminal 54.0fmetal having a bent coniiguration` asfillustratedis attached to a washer 1.5.2

so as vto establish -electrical communication Thus, V-the Vpotentiometer 'itl may be adjusted bysimnle turningrof, the housing 14.

Within thispotentiometer lltl it is preferred Vto incorporate a switch mechanism 58 of the type indicated in Fig. 4 ofvthe drawing. As illustrated openings 60 are pro- Videdwithin an end cap .12 as to carry parts of the switch terminals 62 and 64. These switch terminals end within the ,cavity26 in this end cap V12. The terminal 62 is locatedzso as to tit within an apex or bent portion 64 of agresilient-metal switch armV 66 having sides 67 and 69. This .Switch arm is formed o'that the side 67 is held against the interior of the cavity 26 at all times andso thatthe side69 is held vvagainst the other terminal 64 by means of the exterior of arrotary actuator 68 bearing against a small bentfprojection 7i) formed in the side 69. The actuator 68 is preferably formed of appropriate nonconductive material such as, for example, Ya phenolic 4composition so as to t within the cavity i26 in this end cap 24 -and so as to partially tit within an end of the housing V14. It (the actuator 687) includes a notch y72 whichis'engaged by the projection 38 formed upon Athe interior ,of the housing 14 so as Y therewith. Another notch `74 in the exterior of the ac .rotationof the .housing `L4 so .as

C'this inventionis tObe considered as tuator 68 is adapted to receive the projection 70 during the switch arm 66 to move with essentially a snap action in order to break contact between the terminals 62 and 64 in the obvious manner. Further rotation of the housing 14 of course forces the projection 70 from the notch 74 so as to re-establish contact between these terminals 62 and 64.

An important feature of this invention lies in the fact that both the ridge 2S and the contact element 43 extend around the axis of the potentiometer l0 in a curved path of less than 360 of a circle. Thus, itis impossible with the construction shown for Vthe contact element 48 to engage the resistance element 30 at more than a single point at any one time as the potentiometer 10 is operated. Also, the switch mechanism maybe formed so as to be automatically shut olf when the contact element 48 is not engaging the resistance element 3 4).

As lpreviously indicated during the-use of this potentiometer, the housing 14 -is --rotated land such 'j rotation causes the contact element 4S to engage -diterent portions of the resistance element -36 ove-rlaying'y ythe ridge r28. Those nskilledinthe art to which this vinventionpertains will realize that the curved paths of both the Vridge-28 and the contact element 48 around the axis of the potentiometer l0 permit a degree or type ot' adjustment which can not'be obtained with conventional constructions.

lAs an example ofthis, it is necessaryto refer in more detail to the operation of the potentiometerkltl. -it is possible to' form the curved paths defi-ned by vtheridge 28 :and the contact Velement v43 Vin various fmannei's so thata given amount of rotation of thefhousing 'i4 starting from various positions in which the housing 14 may be located will not produce a corresponding-uniform adjustmentvof an electrical value. Thusfit'ispossibleto provide within the scope of -this invention constructions in Which-rotation-of the housing i4 ata uniformrate causes adjustment -of the potentiometer `1t) lin accordance -with the so-called audiotaperin essence .whatislinvolved is a double functional operation since Aboth the ridge 28 andV the contact element 48 extend in curved paths around the axis of the entire instrumentand since-both ofthese paths may be designed so lasto eac-h provide for a functional adjustment of the entire potentiometerjltl. When so constructed instruments of this invention may be rapidly adjusted by a comparatively small amount or" rotation of'the housings employed.

A number of Vdifferent types of switch mechanisms may Y be incorporated with potentiometersvr failing within the broad scope of this invention. The V-part'icular switch mechanism shown and described is considered todbehespecially adapted for use with instruments kof this invention in View of thenassembly employed Vforthis switch mecha'- nism and in view ofthe fact that the operative Yparts of it may be carried within or upon other vparts of the in- Vstrument of the invention'without Aany 4material change in the-size of these parts. Thevparticularswitch mechanism shown is also consideredadvantageousinasmuchas it issimple and provides an etfectivefsnap action such as is very desirable frorhearingaids.

Qbviouslya wide variety of 4dilerent modications may he made in the instrument shown without departing from the essential features or principles. of thisinvention. As an example of Vsuch modiii'cationthese instrumentsrcan be employed. as `.variable.resistors by simply omitting one of the terminals connected to one of the .ends ofthe resistanceselement employed in anyunit. ious equivalent resistance elements lcan be employed, and various other --means than are .shown can bc' employed for Vattaching theV endca-ps to other parts in assembly. Also-it is obviouslypossihleto omit the switch mechanism shownialthough thisis not considered desirablefrqm Vcommercial and utilitarian reasons. For these reasons being limited .only

.to permit the .side .69. of

by the appended claim, and the claim is to be interpreted in the light of patent doctrine of equivalents.

This application is a continuation-impart of the copending application entitled Adjustable Resistors, Serial No. 598,284, led July 17, 1956.

We claim: A

A variable resistor comprising a pair of spaced apart end caps having a cylindrical mandrel extending between them, said mandrel having a helical ridge formed thereon, resistance wire wrapped around said mandrel and over said helical ridge, a tubular sleeve rotatably mounted on said end caps and enclosing said mandrel, said sleeve having a spiral contact element disposed to wipe on said resistance wire where the latter passes over helical ridge, a stationary washer of conductive material engaging one end of said contact element, and terminal means connected to said washer and to the ends of said resistance wire, said terminal means passing out of said variable resistor through said end caps.

References Cited in the le of this patent UNITED STATES PATENTS 1,216,756 Williams et al. Feb. 20, 1917 2,177,285 Schellenger Oct. 24, 1939 2,266,222 Logan Dec. 16, 1941 2,494,998 Guller Ian. 17, 1950 FOREIGN PATENTS 585,416 France Dec. 9, 1924 1,111,729 France Mar. 5, 1956 

